1. Field of the Invention
The present invention relates to a recording head for discharging ink onto a recording medium and a method for manufacturing the recording head.
2. Description of the Related Art
Recording heads of inkjet recorders include a recording element substrate, which includes a discharge unit for discharging ink, in a nozzle communicating with a discharge port. Known examples of the discharge unit include electromechanical transducers, such as a piezoelectric element, electrothermal transducers, such as a heating resistor, and electromagnetic-mechanical transducers and electromagnetic-thermal transducers for radio waves and a laser.
One of representative recording heads includes an electrothermal transducer as a discharge unit. FIG. 1 illustrates a recording head of this type. This recording head includes a chip unit 6, which includes a flexible circuit board 1, a recording element substrate 3, a frame member 4, and a supporting substrate 5. The flexible circuit board 1 includes a path through which an electric signal for discharging ink is sent to the recording element substrate 3. For example, the flexible circuit board 1 includes copper wiring on a polyimide film. The recording element substrate 3 includes an ink-supply port formed, for example, by anisotropic etching, and an ink path and a discharge port formed by photolithography. The recording element substrate 3, together with the frame member 4 serving as a supplementary member, is mounted on the supporting substrate 5. The recording element substrate 3 is electrically connected to the flexible circuit board 1 through an inner lead 2 disposed on the flexible circuit board 1. This electrically connected portion must be sealed to prevent corrosion and short circuits caused by ink and other extraneous substances. Various types of sealants are used depending on the material and shape of a portion to be sealed and the intended application.
Japanese Patent Laid-Open No. 2001-130001 discloses a technique for sealing a connection between a recording element substrate and a flexible circuit board, in which two different sealants are respectively applied to the two sides of an inner lead.
A sealant is required not only to seal an electrically connected portion, but also not to become detached from the electrically connected portion due to scrubbing with a blade or wiper for cleaning the top surface of a head substrate on which an ink nozzle is disposed or due to contact with paper due to paper jamming. Thus, there is a demand for high-modulus sealants.
Furthermore, a sealant should have a low viscosity (high flowability) to seal the underside of an inner lead. This is because a sealant seals the underside of an inner lead through a very small gap between inner leads. On the other hand, a sealant should have a high viscosity to seal the topside of the inner lead. A sealant must be applied to an inner lead to properly remain on the topside of the inner lead. A sealant having a low viscosity may flow to an unintended portion and may incompletely seal the topside of the inner lead.
Two sealants that satisfy these different requirements have therefore been used to seal the topside and underside of an inner lead, thus making the sealing process complicated. More specifically, after a sealant applied to the underside of an inner lead is heat-cured, another sealant is applied to the topside of the inner lead and is again heat-cured.